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Inside System Storage -- by Tony Pearson

Tony Pearson is a Master Inventor and Senior Software Engineer for the IBM Storage product line at the
IBM Executive Briefing Center in Tucson Arizona, and featured contributor
to IBM's developerWorks. In 2016, Tony celebrates his 30th year anniversary with IBM Storage. He is
author of the Inside System Storage series of books. This blog is for the open exchange of ideas relating to storage and storage networking hardware, software and services. You can also follow him on Twitter @az990tony.
(Short URL for this blog: ibm.co/Pearson
)

On his blog post on preparation, Seth Godin mentioned an appropriate Swedish saying:

There is no bad weather, just bad clothing.

Appropriate because it snowed here in Tucson, Arizona on Sunday evening, leaving many of us here figuring out how to drive through the stuff on Monday. In my entire lifetime, I have only witness snow down in the Tucson valley a handful of times. It got me thinking about coats, and the wonderful schemes for coat check rooms, as an analogy for data access. A lot of people ask me to compare and contrast one technology from another, say block-level virtualization from content-addressable storage, and so on, and I always try to find a good analogy to help explain things.

Let's start with the setting. It is snowing outside and people are wearing coats. When they come inside, they check their coats at a coat check room, a large room with rows and rows of racks with hangers. A coat check attendant takes your coat and puts it on a hanger, and gives you a ticket or other identifier that will allow you to retrieve your coat later. The ticket must have sufficient information to retrieve the coat quickly, rather than searching rows and rows of hangers for it.

Block-based disk storage

You walk to the coat-check desk, tell the attendant to hang your coat on a specific hanger, say hanger number 387. When you come back, you ask for the coat on hanger 387. The coat-check attendant knows exactly where hanger 387 is, and is able to retrieve it quickly. Most disk systems use this approach, including IBM SAN Volume Controller and DS family of disk systems.

Name-based disk storage

You walk to the coat-check desk, tell the person the name that you want to call your coat. An empty hanger is located, and a list of coat names, with their associated hanger number, is then kept. Upon return, you ask for your coat by name, and the coat-check attendant looks up the hanger number to match, and retrieves your coat. This is the scheme used by the IBM System Storage DR550, N series for NAS storage, and the IBM Healthcare and Life Sciences Grid Medical Archive Solution (GMAS).

Content-addressable storage (CAS)

You walk to the coat-check desk and hand them your coat. The attendant weighs your coat, checks the brand, the size, the number of buttons and zippers, types it all in, and the computer spits out a "hash code" from 1 to 99999. An empty hanger is found, and the hash code is associated to the hanger number. Upon return, you provide the hash code you were given, and the coat-check attendant looks up the hanger number to match, and retrieves your coat.This is the scheme used for some non-erasable, non-rewriteable storage, such as the EMC Centera.

IBM invented hash codes in 1953 as a way to speed up searches. For example, if you want to look up a word in the dictionary, knowing the first letter of the word makes it much quicker, because you can thumb directly to that section. A hash code was intended to give a more even distribution, so that if a million words are stored in a "hash code dictionary" then you would calculate the hash code, then look up only that section of words associated with that specific hash code number.

A problem arises when you generate "hash codes" for storage. It is possible for two different pieces of data to resolve to the same hash code. When an application tries to write a piece of data, and it resolves to a hash code that already exists, that is called a collision. One response is to either compare the incoming data to the data that is already stored, confirm they are identical, but that can be time consuming. The other response is to just assume they are identical, and reject the secondary copy, a process often referred to as "de-duplication".

What's the chance of getting a collision for data that is really different? Let's take for example the famousBirthday paradox. Suppose the coat check room assigned the hanger based on your birthday (month and day). How may coats before you run the risk of having two people turn in coats with the same birthday? After only 23 people, the likelihood is 50%. At 60 people, it goes up to 99%.

For this reason, IBM does not offer content-addressable storage. For non-erasable, non-rewriteable storage, the IBM System Storage DR550 requires the application to give each object a name, and that name is then used to storage the data, eliminating the possibility that data might accidently be thrown away.

Shakespeare wrote "What's in a name? That which we call a rose by any other word would smell as sweet." This week my theme will be on names, naming convention, and how we access information on storage.

Take for example these two sentences:

The Bears beat New Orleans.Chicago clobbered the Saints.

Though they appear very different, football fans who might have watched either or both of the two conference title games yesterday would quickly recognize that they refer to the same two teams and the same end-result.

I'll be traveling to Asia next week. While most people call me "Tony", my legal given name is "Anthony" which is what appears on my passport and other legal documents. Most English-speaking countries handle this fine, but it can be confusing in Japan or China, where "A. Pearson" doesn't match "T. Pearson".

In the US, our given and family names are referred to as our "first name" and our "last name", relating to their positional sequence. In Asia, family names come first, followed by their given names last. To help avoid confusion, we have started adopting the practice of putting the family name in ALL CAPITAL LETTERS, so I would "Tony PEARSON" while my colleague may be "WONG Francis".

In Japanese, "Mr. JONES" would be "Jones-san". However, Pearson-san is such a toungue-twister, that most just say "Tony-san" which is fine with me. I have been called "Mr. Tony" in a variety of countries, perfectly acceptable.

You can call me anything you like, just don't call me late for dinner.

Wrapping up my week's theme of "diversity", with posts on a diverse set of topics,today I will suggest ways to spendyour time while you are walking 10,000 steps per day, as recommended by the authorsof the book "You: On a Diet".

(If you thought this was about the 10,000 steps it might take to implement a storage solution, you should switch over to IBM as your storage vendor. For example, the DS3200 and DS3400 can beimplemented in as little as SIX steps. That's pretty cool.)

Blogs like Lifehacker are an excellent resource for neat littletips and tricks to help you throughout your day, like how to use your iPod, cell phone or computer better, for example. These suggestions are based on the idea that you can walk your 10,000 steps with access to an iPod and cell phone.

Learning a language

... or refreshing yourself on a language you might not have spoken in a while. In addition to formal audio-based lessons from Pimsleur, there are podcasts you can get for various languages. In preparation for my upcoming trip to Japan and China, I have been listening to JapanesePod101.com and ChinesePod.com which have quick lessons that complement the formal training.This Lifehacker postindicates there are similar ones for French, Spanish, Italian, and Brazillian Portuguese.

Practicing your presentation

Walking while practicing your 30-60 minute presentation would be good exercise.MicroPersuasion explains how to turn your iPod into the ultimate PowerPoint accessory, and this article in PlayListmag.com providesthe steps to get a PowerPoint presentation onto your iPod. I did this, and the slides are found underPhotos->Photo Library. The images are small, but heck, they are your charts and you should recognize themwell enough to remind yourself what to say on each slide.Also, I am able to record my practice sessions using MP3 Recorder and listen as I page through each slide. (In theory, you can use your iPod to present your slides to your audience, plugging the iPod directly into the laptop projector, instead of a laptop, using cables available at your local Apple store, and use the iPod controls as your forward/backward remote.)

Working your To-Do list

You can download your to-do list to your iPod. I use BackPackIt from 37 Signals. You can sign up for a free account, or upgrade to a paid account, and have anamazingly simple browser-based tool to develop your to-do lists, one for each project or aspect of your life. Oncedone, the list can be emailed to you as plain text. Enable your iPod as an "external disk drive" and copy this text file to your NOTES directory on the iPod drive. Voila! You can now read your to-do list! (I could also send it to my cell phone, using aaaxxxyyyy@tmomail.net, but I find the iPod easier to read and navigate)

Think of something to add? Send an email from your cell phone. With BackPackit, I can send an email that will directly add my text as a note or todo list item. On my phone, this is simply sending a text message to "500" with text like:

"myname@myaccount.com todo # buy bread".

The hash mark (#) separates the subject line from the body of the email, and this is how Backpackit knows its a todo item or a note. If you pre-program the huge email address in advance on your phone, then it isn't as bad as it looks. It will be on your packpackit page the next time you log in.

Well, that's three suggestions. The next time you complain that there is no time to walk, you now have no excuse.

Next week I am "briefing" a client on a variety of topics, everything from our overall strategy, to our DS4000 disk systems, LTO tape, the DR550, and storage virtualization. A lot to cover, and they only gave me 60 minutes!

The challenge is not gathering the material, as it is shrinking it down to cover all the key points into a fluid story. Which reminds me of a saying we have inside IBM: "Develop with prose, Market with poetry." When I was in development, I had to write some huge specifications. Now that I am in marketing, the fewer words the better. In looking to see if this saying was a modified version of a famous quote from someone else, I encountered this interesting quote below. John Windsor of YouBlog might argue this could apply to most marketing attempts just as easily as most poetry.

Most people ignore most poetrybecausemost poetry ignores most people.--- Adrian Mitchell

Roger over at Creative Think asks ifChip Heath is the Next Malcolm Gladwell?, relating to a book called "Made to Stick". I just started reading this book yesterday, but it starts out with how some stories are more memorable than others. Some just "stick" in your head, like songs, and others are quickly forgotten.

I tell a lot of stories, some stick, some don't. For example, I had read in a Barnes and Noble flyer a description of a book that interested me. I went to the store, but had forgotten to bring the flyer with me. When the person at the help desk offered to help me find it on their computer system, I realized that I could not remember the author, the title nor the publisher. The only thing I could remember was that it was a dark green book. It was actually a collection of short stories that were all 55 words in length, all winners of a 55-word story contest. She then took out the flyer itself, and we found it easily from there. She asked why I only remembered that it was green, and I told her: "Because I collect green books."

I am amazed that the writers could cram a setting, characters, plot and resolution into only 55 words, and then I saw Anecdote's post Let's Be Brief which talks about the latest 6-word story contest, inspired by Hemmingway’s shortest story, which was only six words long.

The DS3200 is a 2U high, 12 drive system that attaches to servers via 3Gbps Serial Attach (SAS) interface.You can expand this to 48 drives by added EXP3000 expansion units. Here are theDS3200 specifications.

DS3400

The DS3400 is a 2U high, 12 drive system that attaches to servers via 4Gbps Fibre Channel (FC) interface.You can expand this to 48 drives by added EXP3000 expansion units. Here are the DS3400 specifications.

EXP3000

The EXP3000 is a 2U high, 12 drive expansion drawer. It was announced back in August 2006, but is part of theoverall DS3000 series. It can be used directly with servers, but is also designed to be attached to the back of the DS3200 or DS3400 to increase capacity.Here are the EXP3000 specifications.

With this announcement, IBM provides entry-level storage at the "less-than-$5000" price point, withsupport for intermix of 10K and 15K RPM drives, and scalable up to 14.4 TB capacity.This would be ideal storage for HP, Dell, IBM System x and BladeCenter servers.